1. Field of the Invention
The present invention relates to a mobile terminal and a control apparatus which are used in a packet communications system in which the control apparatus implements routing control of a received packet destined for the mobile terminal.
The present invention also relates to a mobile terminal and a control apparatus which are used in a packet communications system implementing paging control. In the paging control, the control apparatus transmits a paging notification packet to a paging area of the mobile terminal when receiving a packet destined for the mobile terminal, so as to acquire location information of the mobile terminal and to decide a transfer destination of the packet.
The present invention further relates to a mobile terminal and a home agent which are used in a packet communications system in which a plurality of home agents implement routing control of a received packet destined for the mobile terminal, in accordance with each home address and each care-of address.
2. Description of the Related Art
A conventional packet communications system has been configured to confirm reachability of an IP packet, by using the address resolution protocol (ARP) or the neighbor discovery protocol (NDP), prior to the transfer of the IP packet using a unicast address.
The ARP and NDP are defined to associate a link layer address (or a card address) of a network interface card and a network layer address (an IP address) with each other.
Note that an IP address is decided by means of static setting where the IP address is assigned to a network interface card in advance, or by means of dynamic setting such as the dynamic host configuration protocol (DHCP). Alternatively, an IP address is decided by calculation using an address automatic generation technology used in IPv6, based on a network interface card address on a link layer and random numbers.
In the conventional packet communications system, when a mobile terminal (a mobile node or a host) has a plurality of network interface cards as means for allowing a packet to reach its destination, a customer-oriented interface application technology is implemented as an interactive application technology such as an access link manager.
In this customer-oriented interface application technology, for example, a network interface card corresponding to a communication link system having low communication costs is selected among from the plurality of network interface cards.
In such a case, a multiple interface manager (MIM), which manages a plurality of network interface cards, is known as a method of selecting a network interface card autonomously.
The MIM is configured to make a predetermined conditional decision using attributes and measured values collected from each of the network interface cards, so as to select a network interface card to be used.
Conventionally, a packet communications system which implements a mobility management control technology including a Mobile IP technology and an expansion technology of the Mobile IP technology has been known as a communications system which enables transfer of a packet destined for a mobile terminal.
In the mobility management control technology, a home address is used as a controlling unit of packet transfer.
Here, the home address is assigned to each mobile terminal on a home link where a home agent exists, and, for example, the home address is an IP address which belongs to a subnet of the home link.
The packet communications system, which implements the abovementioned mobility management control technology, is configured to perform routing control independently by using each home address as a unit, when a mobile terminal (a mobile node) has a plurality of home addresses as means for allowing a packet to reach its destination, for example, when the mobile terminal is connected to a plurality of home agents depending on application of the mobile terminal and a kind of communications system being used, or when the mobile terminal is in a multi-home situation where the mobile terminal has a plurality of home addresses within the same home agent.
However, in the technique of selecting a network interface card in the conventional packet communications system, an IP address (network layer address) is not particularly considered, and correspondence between the network interface card and the IP address is thus not maintained.
Therefore, the conventional technique of selecting a network interface card has a problem in that address resolution means, such as the ARP and the NDP, is required in order to acquire the abovementioned correspondence, every time a network interface card to be used changes, even among network interface cards to which the same IP address has been assigned.
The conventional technique of selecting a network interface card also has a problem in that an IP address to be used changes when a network interface card to be used changes, so that a procedure for changing a packet's route is required.
For example, in the IPv6 automatic address generation technology using a link layer address, an IP address to be used changes every time a network interface card to be used changes, even where the mobile terminal belongs to the same network domain, so that a procedure for changing a packet's route is required.
Further, even in a case of automatic allocation (dynamic setting) of an IP address by the network side, like the DHCP, a procedure for changing a packet's route is required. This is because network domains generally differ from each other when the kind or owner of the relevant communication link (access link) system is different. Therefore, a IP address to be used changes every time a network interface card to be used changes.
In other words, in the conventional packet communications system, a mobile terminal is required to register an IP address with a control apparatus (such as a routing control agent and a relay agent) within the IP network and with a transmitting terminal, every time a network interface card to be used changes. A packet is reached to the mobile terminal by using the IP address.
Therefore, the conventional packet communications system has a problem in that IP packets related to the aforesaid registration pass through wireless links, so that wireless resources are wasted.
It is highly likely that this problem causes another problem in a paging control technology.
The paging control technology reduces an amount of control signals related to location registration control of the mobile terminal, by registering the location of the mobile terminal per paging area wider than a location registration area, and also reduces power requirements together with an intermittent reception technology of the mobile terminal.
The problem in the paging control technology is that a paging agent cannot acquire location information (subnet) of the mobile terminal accurately.
Meanwhile, the conventional mobility management technology does not maintain the correspondence among a plurality of IP addresses assigned to the same mobile terminal.
Therefore, when an IP packet destined for the mobile terminal is transmitted and the IP packet cannot reach the mobile terminal through a transfer route generated based on a specific home address due to link disconnection or the like, the transfer of the IP packet fails even where a transfer route generated based on a different home address is available and the IP packet could reach the mobile terminal through the transfer route.
Further, the conventional packet communications system does not maintain the correspondence among a plurality of IP addresses, even when the mobile terminal dynamically changes validity and invalidity of the plurality of IP addresses in accordance with applications, communication costs, and power-saving control of network interface cards.
Therefore, the conventional packet communications system has a problem in that a transfer of a packet from a transmitting terminal to a mobile terminal fails.
In such a case, the mobile terminal notifies the transmitting terminal or a name resolution (DNS: domain name system) server of the change between validity and invalidity of the IP addresses by using a control packet, every time the mobile terminal changes validity and invalidity of the IP addresses.
Therefore, the conventional packet communications system has a problem in that resources are wasted according to the frequency of such notification.